The sybase_affected_rows() function seems to work now with the Sybase DB Library. Not sure when this improvement was made, but I'm currently running PHP 4.1.2 on Solaris.

Affected rows seems to return a -1 if the query syntax was incorrect on the last submitted query.Affected rows returns 0 if no rows were affected or another error occured, such as a foreign key violation and also returns 0 if the query was successfully, but no records were affected by the query.If the query was valid and did affect some rows, sybase_affected_rows() seems to be returning the correct number.